GCN Circular 20790
Subject
LIGO/Virgo G275404: iPTF Optical Transient Candidates
Date
2017-03-02T07:29:15Z (8 years ago)
From
Mansi M. Kasliwal at Caltech <mansi@astro.caltech.edu>
M. M. Kasliwal (Caltech), S. M. Adams (Caltech), C. Cannella (Caltech), R.
Lunnan (Caltech), R. Ferretti (OKC), T. Kupfer (Caltech), L. P. Singer
(NASA/GSFC), S. B. Cenko (NASA/GSFC), R. Walters (Caltech), T. Barlow
(Caltech), J. Rana (IUCAA), V. Bhalerao (IIT-B), A. A. Miller
(Northwestern/Adler), Y. Cao (UW), R. Laher (IPAC), F. Masci (IPAC)
report on behalf of the iPTF (intermediate Palomar Transient Factory) and
GROWTH (Global Relay of Observatories Watching Transients Happen)
collaborations:
We performed tiled observations of LIGO/Virgo G275404 (LVC, GCN 20738) and
LIGO/Virgo G275697 (LVC, GCN 20763) using the Palomar 48-inch Oschin
telescope (P48) on the night of 2017-03-01 UTC (delay due to inclement
weather). We imaged 84 fields spanning 633 square degrees, with a 17%
chance of containing the true location of G275404. Of these, 47 fields (361
square degrees) were imaged twice, containing 11% of the probability of
containing G275404, and searched for transient candidates.
During preliminary sifting through candidate variable sources using image
subtraction by our IPAC (Masci et al. 2016) and NERSC (Cao et al. 2016)
pipelines, a total of 140 candidates were saved in the fields imaged.
Applying standard iPTF vetting procedures and removing transients with a
history of previous variability, we flagged 27 optical transient candidates
in the 90% localization contour of G275404, listed below, for further
follow-up.
Name RA Dec UTC R-mag z
Notes
iPTF17bpa 150.966591 1.095135 09:07 18.72 0.0456
specz; off center from host
iPTF17bpb 154.902074 -2.992951 09:25 19.56 0.0511
photz; pstar=0.016; nuclear?
iPTF17bpc 155.671912 -3.647882 09:25 19.31
pstar=0.001; nuclear?
iPTF17bpd 155.181672 -4.163867 09:25 19.28
pstar=0.804; nuclear/stellar?
iPTF17bpk 157.626592 -11.121047 10:20 19.63
nuclear/stellar?
iPTF17bpm 161.324311 -14.376753 10:04 19.26
pstar=0.229; nuclear/stellar?
iPTF17bpn 161.238427 -14.017486 10:04 19.56
pstar=0.46; nuclear/stellar?
iPTF17bpo 158.494163 -12.65084 10:02 19.03
pstar=0.96; nuclear/stellar?
iPTF17bps 161.952768 -15.243493 10:04 19.76
hostless (very slow mover?)
iPTF17bpt 157.657157 -7.372908 09:29 19.49
fading (0.5 mag intra-night); pstar=0.89; nuclear/stellar?
iPTF17bpu 157.559861 -6.799173 09:29 19.81
pstar=0.612; nuclear/stellar?
iPTF17bpy 156.687516 -7.684226 09:29 19.98
pstar=0.933; nuclear/stellar?
iPTF17bqc 158.470076 -11.493302 10:02 19.62
pstar=0.717; nuclear/stellar?
iPTF17bqh 156.749276 -10.358467 10:00 19.49
rising (0.4 mag intra-night); nuclear/stellar?
iPTF17bqi 156.87908 -7.04181 09:29 19.41
pstar=0.962; nuclear/stellar?
iPTF17bqk 162.188261 -15.49746 10:04 19.76
nuclear/stellar?
iPTF17bqz 157.651689 -7.696641 09:29 19.83
pstar=0.885; nuclear/stellar?
iPTF17bro 288.344596 58.81211 10:59 19.82
rising (0.5 mag intra-night), nuclear?
iPTF17brp 291.671757 79.220007 11:47 19.42 0.076
photz; pstar=0.056; off center from host galaxy
iPTF17brr 289.432632 79.995864 11:47 19.88
pstar=0.898; nuclear/stellar?
iPTF17bru 294.594305 63.706556 11:36 19.95 off
center from host galaxy
iPTF17bsd 156.642225 -10.970993 10:00 19.68
rising (0.3 mag intra-night); nuclear
iPTF17bsi 297.077103 78.352918 12:01 19.08 0.014
photz; off center from host galaxy
iPTF17bst 156.998904 -7.216924 09:29 19.87
pstar=0.973; nuclear/stellar?
iPTF17btb 302.938179 72.930472 12:03 18.56
nuclear/stellar?
iPTF17btc 309.740925 72.580678 12:03 18.97
nuclear/stellar?
iPTF17bth 307.33055 68.241724 12:05 19.31
nuclear/stellar?
Positions are stated in the ICRS. Discovery times are noted in UTC hh:mm on
2017-03-01. Magnitudes are based on image subtraction and in the Mould R
filter, calibrated with respect to point sources in SDSS as described in
Ofek et al. 2012.
We caution that many candidates are outside the SDSS footprint and lack a
secure star/galaxy classification for the underlying source. We flag these
as "nuclear/stellar?". Where available, we provide machine-learning
probability scores on whether the underlying source is a galaxy/star (0/1)
(Miller et al. 2016).
We encourage spectroscopic classification of these candidates. In
particular, we highlight iPTF17bpt, iPTF17bqh, iPTF17bsd as fast-evolving
by more than 0.3 mag in the same night; iPTF17bpa and iPTF17bsi as local
transients (d < 200 Mpc), and iPTF17bpa and iPTF17btb as bright transients
(m < 19 mag).
We are grateful to the Palomar crew (especially John Henning, Jeff
Zolkower, Carolyn Heffner, Jamey Eriksen, Nick Ganciu) for their hard work
in reviving a faulty declination encoder essential to collecting this
dataset during the last two days of iPTF survey operations.